Straying a little outside my normal world, but the TSO's priority will be to minimise the disturbance on their system, which means having sufficient transformer impedance to decouple the EAF from the transmission substation. With (I'm guessing a little here) 15% - 20% impedance you're looking at a substantial fault current on the LV side and if there's a fairly direct connection to the transmission system then the EAF transformer impedance is going to be the dominant factor in determining the fault current.
Hopefully someone like prc will have a bit more knowledge of EAF transformers themselves, but my understanding isn't so much that the fault level is abnormally high as the transformer and ancillaries like the tapchanger are designed to handle sustained and repetitive fault-level currents on a more-or-less continuous basis.